Over the years, many stair climbing apparatuses that climb and descend stairs on their own have been developed, especially for use with or as wheelchairs. Some of them use tracks, like in Canadian patents Nos. 1,194,775 issued on 8 Oct. 1985, 1,283,668 issued on 30 Apr. 1991, and 1,298,586 issued on 7 Apr. 1992. Others use a plurality of wheels, like in U.S. Pat. No. 3,438,641 issued on 15 Apr. 1969, and U.S. Pat. No. 3,592,282 issued on 13 Jul. 1971, and Canadian patents Nos. 1,261,726 issued on 26 Sep. 1989, 1,275,296 issued on 16 Oct. 1990, and 1,313,891 issued on 23 Feb. 1993. Other examples of stair-climbing and descending mechanisms are disclosed in U.S. Pat. No. 3,227,465 issued on 4 Jan. 1966 and U.S. Pat. No. 4,618,155 issued on 21 Oct. 1986.
Also known in the art is U.S. Pat. No. 468,022 (Bray) issued on 2 Feb. 1892 and relating to a stair-climbing perambulating chair. Bray discloses a chair comprising screws to lift the chair vertically and a rack-and-pinion arrangement to advance the chair horizontally. However, one drawback of Bray is that the mechanism is so bulky and cumbersome that it is on the sides of the chair, thereby resulting in a chair wider than conventional.